具可調式耦合器之超導多量子位元系統的磁通串擾特性分析與抑制

Abstract

現行的超導量子位元架構越來越多採用包含可調耦合器的系統，以便在未執行雙量子位元閘操作時，能有效關閉相鄰量子位元間的耦合，從而達到更佳的雙量子位元閘保真度。然而，由於可調耦合器通常不具備獨立的量測線路，使得整體磁通串擾的量測與分析變得困難。 本研究針對由多顆可調式 transmon 量子位元與耦合器所構成之超導量子系統，進行磁通串擾效應的量化分析與補償技術開發。透過 Two-Tone Spectroscopy 與 Ramsey 干涉法建構磁通串擾矩陣，並搭配線性模型進行偏壓映射與補償參數提取，成功將非預期耦合導致的磁通串擾抑制至O(10−4 )。補償後系統具備更佳的頻率可控性，顯著提升元件間的獨立操作能力。此外，我們亦展示補償機制能促進 CZ gate 操作點之辨識。並藉由比較不同封裝方式下的樣品設計，指出控制線接地處理對於抑制近距離磁通串擾具顯著影響。

Modern superconducting quantum processors increasingly adopt architectures incorporating tunable couplers, which allow the effective decoupling of neighboring qubits when two-qubit gates are idle, thereby improving two-qubit gate fidelity. However, since these couplers typically lack independent readout lines, it becomes challenging to characterize the overall flux crosstalk in such systems. This thesis investigates flux crosstalk in a superconducting quantum processor composed of multiple frequency-tunable transmon qubits and couplers. By constructing crosstalk matrices using the Two-Tone and Ramsey measurement, and applying a linear compensation model, we successfully suppress unintended magnetic coupling to O(10−4 ). The compensated system exhibits improved frequency controllability and enhanced orthogonality of the bias control lines, enabling more independent operation of individual components. Furthermore, we demonstrate that the compensation procedure facilitates the identification of CZ gate operating points. Finally, by comparing different packaging configurations we analyze the impact of wire bonding on flux crosstalk.